In manufacturing, a critical, time-limiting step for many products is the design and fabrication of “tooling,” including molds and dies. Complex dies may take from weeks to a year to perfect prior to manufacture of a product. In present manufacturing processes, added steps are necessary to overcome existing fabrication methods. For example, molds and dies must be machined to provide cooling channels and an acceptable surface finish.
Traditional materials and fabrication methods used to manufacture tooling plastic or metallic prototype or production parts, utilize homogenous wrought or cast tool steel alloy materials which, when machined, heat treated, finished and assembled, form a mold, die or other component. In many cases, the application requirements within a mold or die component differ, resulting in a reduction in die life requiring repair or replacement of the die or mold.
In an effort to facilitate the fabrication die components and/or to accommodate variations in application requirements, dies and molds often include multiple components. Each section or mold component is fabricated from a homogenous metal alloy, which results in homogenous material properties within each die or mold component. The variation in material property requirements within a mold or die component, results in localized wear or and premature failure of the mold or die component in the areas which the application requirements exceed the material properties (mechanical and physical properties) inherent to the homogenous metal alloy.
In many cases, molds or dies are assembled and comprised of component parts to achieve the need for a variation in material properties within a mold or die. For example, section and insert may be fabricated from dissimilar materials, or processed differently, as through heat treatment.
It has long been recognized that additive processes, wherein material layers are built up, could potentially be beneficial in the fabrication of tooling by eliminating multiple component parts or fabrication steps. However, known processes which deposit metal result in a sintered product, due to trapping of oxides and inadequately bonded material. One such process is laser cladding, wherein a laser is used to generate a melt-pool on a substrate material while a second material, typically a powder or wire, is introduced, melted, and metallurgically joined.
Cladding is generally distinguished from alloying on the basis that cladding melts a relatively small amount of the base substrate material relative to the amount of the deposited material, and the powder system delivers a controlled volume of metal particles into this molten volume. The particles become dispersed throughout this molten volume and form a deposition of a desired composition on the outer layer of the substrate. Removal of the laser beam from the molten volume, such as by advancement of the substrate workpiece relative to the focal point of the beam, causes the molten volume to be rapidly chilled. The chilling occurs so rapidly that the volume often retains the characteristics of the molten mix.
Conventional laser cladding techniques move the metal article relative to the focal point through the use of jigs, parts handlers, and the like. The beam focal point therefore remains fixed in space, as does the powdering point. Uniform movement of the metal article usually requires a complicated jig which is difficult to manufacture, very expensive, and usually not very successful, particularly with intricate geometries. For this reason, laser cladding of metal parts having other than relatively flat geometries have been nearly impossible to achieve on a consistent uniform basis.
Close control of dimensions is necessary for the production of parts and tools having close tolerances, acceptable microstructures and properties, and which can be produced at a reasonable cost and within a reasonable period of time. A solution to the problem involves the use of feedback-controlled, direct metal deposition (DMD) as described in U.S. Pat. No. 6,122,564, the entire contents of which are incorporated herein by reference. With DMD, a laser is used to locally heat a spot on a substrate, forming a melt pool into which powder is fed to create a deposit having a physical dimension. Optical detection means, coupled to an optoelectric sensor, are used to monitor the physical dimension of the deposit, and a feedback controller is operative to adjust the laser in accordance with the electrical signal, thereby controlling the rate of material deposition.
Preferably, the monitored physical dimension is the height of the deposit, and the system further includes an interface to a computer-aided design (CAD) system including a description of an article to be fabricated, enabling the feedback controller to compare the physical dimension of the deposit to the description and adjust the energy of the laser in accordance therewith.
A DMD system for automatically fabricating an article typically includes a computer-aided design database including a description of the article to be fabricated, a work table for supporting the substrate, and translation means for moving the substrate relative to the laser and a raw material feeder. In one arrangement, the worktable moves while the laser and feed means remain stationary, whereas, in a different configuration, the laser and feeder move while the work table remains stationary. As a further alternative, both the laser/material feed and work table/substrate could be moved simultaneously, preferably under feedback control.
One distinct advantage of DMD is that material composition may be varied during the deposition process. As disclosed in co-owned U.S. Pat. No. 6,472,029, DMD is used to fabricate composite material structures which provide a combination of desirable physical and mechanical properties. In particular, the use of DMD facilitates the production of high-strength, abrasion-resistant laminate structures which also exhibit a high degree of thermal conductivity. In particular, DMD is used to deposit alternate layers or rows of a thermally conductive material, such as copper or a copper alloy, and a high strength, abrasion resistant thermal barrier material, such as tool steel. The resulting composite material structure has mechanical properties (i.e., yield strength, hardness and abrasion resistance) which exceed that of pure copper or copper-based alloys required for mold materials, thereby enhancing productivity while improving part quality in these and other applications.